Strain reliever for electrical conductors



Oct. 7, 1941. G. WALKER STRAIN RELIEVER FOR ELECTRICAL CONDUCTORS Filed April 12, 1940 m E/ a m M F m M x No e 6% Patented Oct. 7, 1941 UNITED STATES PATENT OFFICE 2,258,343 STRAIN RELIEVER. FOR ELECTRICAL connoc'rons George Walker, Passaic, N. J. Application April 12, 1940, Serial No. 329,264

6 Claims.

This invention relates to improvements in means for relieving mechanical strain from the electrical connections of the usual extension cords for electrical toasters, fiat irons and other devices, and has for an object the provision of a device which will simply and positively relieve mechanical strain from the connection between the terminals of the cord and the contacts to which they are connected so as to prevent dam age or breaking of same.

In the usual electrical appliance plug, for example, the conductors of the cord pass through an opening in the end formed by the two parts of the plug when assembled and then around op- I posite sides of a partition molded integrally with one of the parts of the plug to the usual contact members to which they are secured by means of small screws or binding posts. It is sometimes customary to tie a simple knot in the two conductors before making the electrical connection in order to provide a mechanical stop within the plug to absorb the mechanical strain set-up when the plug is disengaged from its socket by sharply pulling the cord. 7

Therefore, it is a further object of my invention to make a simple strain relieving device which will eliminate this knot and thus effect considerable saving in the length of the conductors of the extension cord. I

Another object of my invention is to provide a strain relieving device which will meet at the requirements of the Underwriters"Laboratories which'includes withstanding, for a period of one minute, a straight pull of 50 pounds between'thecord and the plug with the conductors entirely disconnected from the aforesaid contact screws, and also withstanding, for a period of one minute,

a prescribed torque between the cord and the plug.

My device not only meets these requirements easily, but provides a large factor of safety.

A further object is to provide a simple device of this character which can be readily attached to the cord and securely fastened in position by means of a simple hand tool, or if such a simple tool is not available, then the device can be securely applied with an ordinary pair of pliers.

In addition, I provide a device which besides being most eflicient and useful, gives a pleasing and attractive appearance. e Lastly, when my device is used the rubber insulation of the conductors is surrounded by a strong wafer of insulating material, so that should suchjrubber insulation deteriorateinvtime,

the insulating wafer or disc will not increase the possibility of short circuiting, but will supply a measure of protection against short circuits.

I accomplish all of these objects with a very simple device easily manufactured and assembled and exceedingly inexpensive.

With the above and other objects in View, the invention may be said to comprise and device shown in the accompanying drawing and hereinafter described and particularly claimed to gether with such improvements and modifications thereof as will be made obvious by this description to those skilled in the art to which the invention relates.

Reference should be made to the accompanying drawing forming a part of this specification in which- Figure 1 is a plan View of my strain relieving device mounted in position on an extension cord and located in the annular recess of an ordinary heater plug.

Figure 2 is a sectional view of my strain relieving device secured on an extension cord and showing the deformation of the conductor insulation and with a portion of the clamping member broken away.

Figure 3 is a plan View of the device of Fig. 2 completely assembled and in its opened or unattached position with a portion of the clamping member broken away.

Figure 4 is a plan view of a modification of the device to resist torque or turning movement of the inner Wafer with respect to the outer clamping member.

Figure 5 is a plan View of another modification of the same device which may be securely locked to the extension cord or in some cases may be so constructed that the outer clamping member may be rotated with respect to the inner insulating wafer.

As shown in Figure 1, the usual extension cord or twin conductoral passes through opening 2 in the end of the usual heater plug in the usual way and then divides so that each conductor may pass on either side of a small partition and be attached to the contact pieces with the usual small attaching screws (not shown).

In the end of the heater plug is the usual annular recess 3 in whichis located my strain relievingdevice 4 se curely attached to the extension cor'd so as to'prevent any longitudinal movement of the extension cord with respect to such plug. Thus, if a heavy strain is imposed on the extension cord, such as by pulling or jerking on the cord to remove the heater plug from its socket, this strain is taken up by the device and immediately transferred to the shell of the plug, thus removing all tension or strain from the contacts.

In the past one method of attaining this result has been by tying a simple knot in the ends of the two conductors of the extension cord, with such knot located within the body of the heater plug. This expedient shortens the extension cord and prevents the full use of the length of the conductors. My device eliminates this expedient and permits the use of the full length of the conductors, and in addition, my device checks or prevents the unraveling of the braiding on the extension cord. Further, my strain relief holds the braiding firmly in place with respect to the underlying rubber insulation so as to prevent any movement of the braid cover along the extension cord.

As will be seen from Figure 3, my strain relieving device consists of a small U shaped channel member 5 with the channel facing inwardly, made of suitable metal capable of being deformed but without temper or springiness, such as soft tempered malleable steel or the like. If it is desired, this member may be plated to improve its appearance.

An insulating disc-like piece or wafer comprising connected portions 6 and I are inserted Within the U shaped channel. This insulating piece is made of strong, tough, yet fracturable, insulating material, such as Bakelite, fibre or the like, and at the junction of members 6 and T has two oppositely opposed notches or cut-away portions 8 and 9 to provide a weakened portion at this point. Thus, when the legs of the clamping member 5 are urged toward each other in applying the device, the insulating material being fracturable, breaks at this point so as to permit the insulating members 6 and l to move towards each other and tightly grip the insulation of the extension cord. In Figure 2 the dotted circle ID indicates the normal diameter of the extension cord, while the solid section shows how the cord is compressed and tightly gripped between the inner edges of insulating members 8 and I so that there is no possibility of slipping.

In the form of the device shown in Figures 2 and 3 the tendency of the insulating members 5 and 'l to turn in the clamping member 5 when the cord is twisted, is eliminated because, when the two members 6 and I have been clamped to a cord, they combine to form a tear drop shape which, as will be seen from Figure 2, cannot possibly turn inside of the similarly-shaped clamping channel 5, Also, with this particular shape when the device is mounted in the annular recess 4 of the heater plug, the sharp edges at the ends of the clamping legs effectively prevent the entire strain relieving device from turning within such recess.

The same result may be attained by means of the modified structure of Figure 4 in which insulating members 13 and M are provided with two projecting tips II and i2 whose function is to prevent turning between the insulating members l3 and I4 and the outer metal clamp 5, even when clamp 5 has been bent into a perfect circle as shown.

It will be immediately apparent that when the device shown in Figure 5 is properly secured to the extension cord, the locking action of the metallic clamp and the friction between the parts serves to hold my device securely in position as a strain relieving device.

However, in some instances it may be desirable to permit turning movement between the insulating members and the outer clamping member. In such case and with the tips I l and I2 omitted, it is possible to proportion the parts so as to lessen friction therebetween and result in the structure shown in Figure 5 in which the insulating members 15 and 16 combined are annular and may turn within the annular clamping member 5.

The extreme simplicity of this device will be immediately apparent as well as its attractive and compact appearance. Once attached, there are no moving parts and the device is simple, rugged and durable.

My strain relieving device can be readily attached to extension cords by a simple form of hand-operated tool to apply the necessary compressive pressure to the outside of the metallic clamping member 5. As a matter of fact, in the absence of such a tool, an ordinary pair of pliers will serve the purpose.

It will be evident that the device may be applied to other kinds of electrical equipment in which it is desirable to remove mechanical strain from the ends or any other part of a conductor, simply by applying one of the devices at the desired point and providing an abutment against which it can rest when under strain.

It will also be evident that the device, while extremely inexpensive to manufacture and apply, is strong and highly effective for its purpose and that it in no way endangers the insulation of the cord, since its only contact therewith is through members composed of insulating material.

I claim:

1. A strain reliever for an electrical conductor, which consists of a U-shaped wafer of insulating material which is fracturable into two parts which can be brought together to assume a washer-like shape and grip the insulation of an electrical conductor and a distortable non-resilient metal rim surrounding the outer edge of said wafer both before and after application to said conductor and forming means for fracturing said wafer and for retaining it in insulation-gripping position.

2. A strain reliever for an electrical conductor, consisting of a U-shaped wafer of insulating material having a fracturable portion midway between its legs so that the ends of said legs can be brought together to form a two-piece clamp around an electrical conductor, and a distortable, non-resilient metal rim surrounding the outer edge of said wafer both before and after fracture and comprising means for fracturing said wafer and for retaining it in clamping position.

3. A strain reliever for an electrical conductor, consisting of a U-shaped wafer of insulating material having opposed notches midway between its legs to define a line of fracture so that the ends of said legs can be brought together to form a two-piece clamp around an electrical conductor, 'and a relatively stiff non-resilient metal rim surrounding the outer edge of said wafer which can be bent to bring the ends of said legs together to retain them substantially in contact with each other.

4. A strain reliever for an electrical conductor which consists of a U-shaped wafer of insulating material having a fracturable area between its legs, means for fracturing said wafer and causing the resultant portions to assume and retain a substantially ring-like shape, said means consisting of a non-resilient distortable metal rim closely surrounding the outer edge of said wafer.

5. A strain reliever for an electrical conductor which consists of a U-shaped wafer of insulating material having a fracturable area between its legs, means for fracturing said Wafer and causing the resultant portions to assume and retain a substantially ring-like shape, said means consisting of a non-resilient distortable metal rim closely surrounding the outer edge of said wafer both before and after fracture.

6. A strain-reliever for an electrical conductor, which consists of a U-shaped wafer of insulating material which is fracturable into two parts which 10 can be brought together to assume a washer-like shape and grip the insulation of an electrical con- 

